We are developing, testing and using Akeeba Subscriptions using the latest version of Joomla! and a popular and actively maintained branch of PHP 7. At the time of this writing this is:
Joomla! 3.8
PHP 7.2
Akeeba Subscriptions should be compatible with:
Joomla! 3.8.
PHP 7.0, 7.1, 7.2.
Changelog
Select the default payment method if no or an invalid method was selected (instead of simply failing)
Joomla! 3.9 backend Components menu item compatibility